Butadiene production by the pyrolysis of dilsopropyl



Patented May 29, 1945 BU'i'ADIENE PRODUCTION BY THE PYBOLYSIS OF DIISOPBOPYL Edmond L. dOuville and Alex G. Obiad, Chicago,

Ill., assignors to Standard Oil Company, Chicage, 111., a corporation of Indiana No Drawing.

Application July 13, 1942,

Serial No. 450,799 a 3 Claims. (01. zco-cso) This invention relates to the production of butadiene from hydrocarbon charging stocks and it pertains more particularlyto a. new and improved method of butadiene production involving the pyrolysis or demethanation of diisopropyl. (2,3-dimethylbutane) Butadiene has been prepared in small amounts by pyrolysis of various hydrocarbons but always with low yields and large gas production. The most outstanding results heretofore obtained by the pyrolysis of saturated hydrocarbons required the use of cyclohexane as a charging stock. -An object of our invention is to provide a method of producing butadiene from hydrocarbon charging stocks which will produce'larger butadiene yields than any heretofore obtainable. A further object is to minimize the production of other C4 hydrocarbons and to minimize polymerization and secondary reactions in the diisopropyl pyrolysis step. A further object is to provide a process which will minimize the problem of recovering butadiene from conversion products. Other objects-will be apparent as the detailed description of the invention proceeds.

We have discovered that large yields of butadiene can be obtained by the thermal pyrolysis of diisopropyl. Diisopropyl does not occur in any significant amounts in crude petroleum or in the ordinary distillation products thereof, crude light naphthas containing only about .01 to 2%. It may, however, be synthetically produced by the alkylation of isobutane with ethylene in the presence of an aluminum halide catalyst. It ma also be obtained by various methods of chemical synthesis. We prefer, however, to'employ the isobutane-ethylene alkylation process for the pro-. duction of the diisopropyl because this process has been found to be commercially practical for producing large yields of the diisopropyl at relatively low cost. I

Diisopropyl is unique among the hydrocarbons now available or likely to become commercially available for butadie'ne manufacture in that the its pyrolysis is the much desired butadiene. Actual pyrolysis of this hydrocarbon has shown, however, that'unless conditions are carefully controlled. there will be considerable amounts of isobutylene and other products formed because of secondary reactions. By using, carefully controlled conditions, however, we can obtain large. yields of butadiene and a minimum of undesirable products. y

We may obtain diisopropyl from any source whatsoever but we preferably obtain it by the isobutane-ethylene alkylation reaction with an aluminum chloride catalyst. The charging stock need not, of course be pure diisopropyl but it should be rich in diisopropyl, i. e., should contain.

, at least 20 to 50% of it and preferably should contain more of this than any other hydrocarbon in its composition, the higher the diisopropyl content, the better for our purpose. The chargin butadiene can be further purified if necessary bymain primary C4 product which can result from stock is subjected to pyrolysis at a temperature of the order of about 1200 to 1650 F., preferably within therange of 1350 to,1550 F., with a reaction time of the order of .01 to 10 seconds, ordinarily below 5 seconds and preferably in the general vicinity of 1 second or less, and at a pressure of the order of .1 to 10 atmospheres, preferably as low asis commercially feasible. An inert diluent such as steam, carbon dioxide, nitrogen, etc'. may be employed for repressing undesirable secondary reactions and a quick cooling or quenchingis likewise preferably employed for the same purpose. The total product may be injected into water, or it may be absorbed in a naphthe or other hydrocarbon oil having an initial boiling point substantially above" the boiling point In the latter case the rich Jabwhich a cut rich in butadiene may be recovered therefrom by simple distillation and unconverted diisopropyl can be recycled to the process. The

conventional methods.

For obtaining the diisopropyl. isobutane may be allcvlated with ethylene at a temperature within the approximate range of 0 to 250 F., preferably within the more limited range of about 50 to 150 F., for example about to F. .The pressure for such alkylation may be within the approximate range of atmospheric to 1000 pounds per square inch but preferably is in the more limited range of about 50 to pounds per square inch and should be suflicient to maintain the reactants in liquid form. The catalyst forthe alkylation is preferably an aluminum chloride-hydrocarbon complex containing within the approximate range of 23m 32%, for example 28% of bound hydrocarbon. This complexis prepared.

active aluminum. Asa specific example of diisopropyl preparation about four parts by weight of uct from this reaction contains about 70% of Ce' hydrocarbons of which about 88% is diisopropyl and 12% is Z-methyl pentane. It is preferable to maintain an excess of isobutane in this alkylation reaction since an excess of the ethylene would lead to theformation of polymer products. The mol ratio of isobutane to ethylene should be greater than 1:1 and should preferably be at least about 3:1 to 4:1 or higher.

iWhile we prefer to employ the aluminum chloride-hydrocarbon complex as a catalyst it should be understood that we may simply employ aluminum chloride or aluminum bromide ,per se and still obtain substantial yields of Ce hydrocarbons containing substantial amounts of diisopropyl. Where pure aluminum chloride is employed as a catalyst under the conditions referred to in the above example, the stabilized liquid product yield is lower, the Ca hydrocarbon content of the liquid products is substantially lower (only about 45% instead of about 70%) and the diisopropyl content of the Ca fraction is likewise substantially lower (about 45 volume percent as com pared to 88 volume percent). Nevertheless, diisopropyl could be produced by aluminum chloride per se or by an inorganic aluminum chloride complex such as sodium aluminum chloride,

lithium aluminum chloride, etc. Generally speaking, any Friedel-Crafts type catalyst may be used,

particularly aluminum halide catalysts which include pure aluminum halides as well as catalyst complexes. When pure aluminum chloride is employed itis desirable to use lower temperatures or to employ an inert solvent or diluent for suppressing undesirable side reactions. vAn activator such as a hydrogen halide exemplified by hydrogen chloride, hydrogen bromide, etc. may be employed particularly in a. continuous alkylation process where catalyst or aluminum chloride is continuously added to the reactor but activators are not. as essential in, this alkylation process as they are in the aluminum chloride isomerization hydrocarbons. If propylene and butenes are present in the alkylation reaction the resulting alkylate will be C1 and Ca hydrocarbons respectively which may be easily separated from C hydrocarbons (diisopropyl) by simple fractional distillation. The alkylation process may, of course, be batchwise, multi-stage or continuous. For converting the diisopropyl into butadiene we prefer a charging stock containing as high 'a. percent of diisopropyl as is commercially feasible although it is not necessary of course that thediisopropyl be absolutely pure. A Cc fraction from an isobutane-ethylene alkylation containing from about to 90% diisopropyl is a preferred charging stock. Crude petroleum and the distillation products thereof contain too small amounts of diisopropyl to be of any significance in our process. The crude petroleum fractions, even close out fractions, heretofore subjected to pyrolysis at high temperatures yielded only about 2% of butadiene and gave a dry gas production of about ten to twenty times the butadiene production. In our process the dry gas production is minimized and high yields of butadiene are produced.

The diisopropyl charging stock (for example the Cc fraction from isobutane-ethylene alkylation) is rapidly heated to a temperature of the order of 1200 to 1650" F., preferably to about1350 to 1500" F. and the diisopropyl is maintained at this high,

temperature for a very short period of time, preferably in the presence of an inert diluent in order to avoid polymerization or other secondary reac-- tions. The duration of the high temperature pyrolysis step, or the so-called time of contact, should be within the approximate range of .01 to 10 seconds and is preferably of the order of 1 second or less. A diluent such as steam, carbon dioxide, nitrogen, or the like, may be employed in large amounts, for example about 80% based on charging stock. In addition to employing the short time of contact and the diluent for avoiding secondary reactions we employ quick cooling or quenching. Thus the hot reaction products may be injected into water or oil or other quenching liquid for obtaining substantially instantaneous cooling in order to further safeguard against secondary or other side reactions. Relatively low pressures should be employed generally within the range of about .1 to 10 atmospheres, for example, approximately atmospheric temperature.

It is essential in the diisopropyl pyrolysis step to avoid polymerization of the ethylene or primary pyrolysis products (including the butadiehe itself), hence the reaction is preferably carried out in the absence of conventional cracking catalysts since such catalysts have a polymerizing action, particularly under the conditions hereinabove set forth. We do not, however, necessarily exclude the use of catalysts such as calcium aluminate or contact materials since contact materials may serve an important function in obtaining effective heat transfer for the thermal pyrolysis and may, in fact, prevent to a certain extent undesirable isomerization and polymerization while promoting the demethanation of diisopropyl. Examples of contact materials which may be employed include Monel metal, steel filings, carbon rings, carborundum, but generally speaking our process does not require the presence of such contacting agents.

When diisopropyl is subjected to pyrolysis at temperatures substantially below about 1200 F.

the butadiene production is too low to be of commercial significance. However, at a temperature of about 1400 F. and with a short contact time we have produced about half again as much butadiene as was produced by the pyrolysis of cyclohexane under the same operating conditions.

A preferred example of our process is substantially as follows! a charging stock consisting essentially of diisopropyl is vaporized and admixed alloy tube heated by the usual means, for exama,s7o,se 1 1 pie, radiant energy from glow bars, incandescence or other quenching liquid to avoid secondary or side reactions. The resulting products may be fractionated by conventional means and it will be found that large yields of butadiene may be obtained along with considerable amounts of methane and smaller amounts of other hydrocarbon gases.

"While we have' described indetail a preferred embodiment'of our invention and preferred operating conditions there for, it'should be understood that our invention is not'llmited to the specific details hereinabove set forth since various modifications and alternative procedures and conditions will be apparent from the above description to to those skilled in the art.

We claim:

1. The method of producing butadiene which its compositionand containing at least. 20% of dusopropyl to a temperature within the appr ximate range of 1200 to 1650? F., subjecting said charg n stock to said temperature for a period of time within the approximate range of .01 to 10 seconds, maintaining the charging stock at a' pressure'within the approximate range of .1 to 10 atmospheres during the heating step, immediate- 1y quenching the products leaving the heating step and fractionatlng the products to recover butadiene therefrom.

2. The method of claim 1 whereinthe dura-' tion of the high temperature treating step is in the general vicinity of one second.

3. The method of producing butadiene which comprises subjecting a-charging stock containing at least 50% by weight of diisopropyl to a temperature in the approximate range of 1350, to

' 1500 F. in the presence of a large amountof diluent gas for -a time of contact in the generalvicinity of one second and at a low pressure for demethanating the diisopropyl and forming butadiene as primary conversion-product and immedicomprises heating a charging stock containing.

- morediisopropyl than any other hydrocarbon in ately quenching the conversion products to prevent polymerization and secondary reactions.

EDMOND L. D'OUVIILE. ALEX G. QBLAD. 

